Various types of hearing aids and hearing enhancement apparatus are known in the prior art. Some of these devices utilize the transmission of sound waves through the air from the device to the human sensory system, such as to the cochlea, and others utilize other media such a vibratory contact with the body as the medium of transmission. For example, in U.S. Pat. No. 4,982,434--Lenhardt et al., there is disclosed a hearing enhancement device which utilizes direct vibratory contact with the human body and transmission of modulated ultrasonic sound waves within the body, such as though bone conduction, as the medium of stimulating the hearing response. Other types of hearing enhancement devices utilize transmission of sound wave waves through the air for interaction with the cochlea as the medium of stimulating the hearing response.
Some of these prior art systems utilize digital signal processing to perform various functions in the hearing enhancement process. However, the use of digital technology in miniaturized, light weight, portable hearing enhancement devices that can be carried on the person and worn in low visibility mounting arrangements has been severely limited because of the high cost and complexity of the digital circuitry and the high power consumption required for the full implementation of desired functions.
In addition, in the case of electronic circuitry of all types as applied to such types of prior art devices, once the circuitry is embodied in the apparatus, the characteristics provided thereby remain fixed and therefore the adaptability of such prior art devices to custom applications and to the specific needs of particular patents has been limited.
It is an object of the present invention to overcome these disadvantages of the prior art, particularly in relation to the utilization of digital technology in hearing enhancement devices.
It is also an object of the present invention to provide a simplified and inexpensive digital frequency response analyzing and shaping apparatus and method which detects the instantaneous frequency of a signal and converts the same to a transform and which adjusts the amplification of the signal over a frequency spectrum as a function of the frequency dependent transform.
It is a further object of the present invention to provide an apparatus and method for customizing a frequency dependent signal amplification characteristic which matches and compensates for the deficiencies in the hearing response of a particular patient and which can be field programmed at the point of application based on the measured hearing characteristics of the patient and set in a programmable memory in the form of a patient prescription table (PPT).
It is also an object of the present invention to provide a simple and inexpensive digital apparatus and method for determining the instantaneous frequency of a time varying signal in a manner that is much simpler than methods based on Fast Fourier Transforms and similar methods known in the art.
It is a further object of the invention to provide an innovative author-friendly experimental platform for testing and evaluating the psychophysical effects of enhancement methods, known and unknown, in the present state of the art. The invention enables program changes in situ that control and modify system behavior extensively, including even the addition of new processing features.